Generally, upright pianos incorporate a series of piano action assemblies each corresponding to a key. Each action assembly is arranged such that the depression of a key causes a hammer associated with the piano action assembly to strike a corresponding string of the piano.
In conventional upright piano actions this is achieved by having the hammer assembly arranged in a relatively upright orientation with a butt at its lower end which is rotatably mounted on the main action rail. The hammer assembly also incorporates a hammer head remote from the butt and is arranged to rotate from a rest position to a string striking position wherein the hammer head strikes the string.
The hammer assembly is caused to rotate on depression of the key by an assembly incorporating a wippen and a jack. The jack interconnects the wippen and the hammer butt and is arranged to engage the hammer butt at its lower end at a position off set from the point of pivot of the hammer butt. The jack is caused to apply an upward pressure on the hammer butt when in the rest position which causes the hammer butt to rotate from the rest position to the string striking position. The jack is caused to apply this upward pressure by depression of the key which imparts a force through the wippen to the jack.
Furthermore, the jack is caused to disengage from the hammer butt as it rotates from the rest to the string striking position. The point at which this occurs is the "set off" point and the pressure that is required on the key to cause the jack to disengage is called the "set off" pressure.
Biasing means act on the hammer butt to return the hammer from the string striking position to the rest position. In addition, a jack spring acts on the jack to cause it to re-engage the hammer butt once it has disengaged the hammer butt.
A player of the piano is able to sense the "set off" point because as the hammer rotates under the influence of the jack, a resisting force is applied to the hammer butt by the biasing means. This resisting force is transmitted through the jack and wippen to the key. However, on release of the jack from the hammer butt, this resisting force is no longer transmitted to the key. Therefore, as the jack is released from the hammer butt, the player senses a changing of pressure on the key.
To enable the jack to re-engage the hammer butt it is necessary to either completely release the key or the jack spring has to be highly tensioned such that it overcomes the biasing force acting on the hammer butt. If the jack spring does impart a force which is greater than the biasing force, then the key does not have to be fully released, as the jack spring is able to rotate the hammer butt towards the string striking position to a position wherein the jack is able to re-engage the hammer butt.
In the repetitive playing of a piano, the keys are not fully released. Consequently, if a piano is to have good repetitive playing characteristics, the piano should be arranged such that the jack spring is tensioned to a level that is greater than the biasing means when the hammer butt is near the rest position to enable the jack to re-engage the hammer butt without the key being fully released.
In conventional upright pianos, to enable good repetitive characteristics, the biasing means has been arranged to apply a relatively low force on the hammer. In this way the jack spring is able to overcome this force to enable the jack to re-engage the hammer butt when the key is not fully released.
However, by having the biasing means only apply a relatively low force on the hammer butt, the pressure transmitted to the key by the resisting force of the biasing means as the hammer rotates from the rest to the string position is low. Consequently, the "set off" pressure is low and the "set off" point is not clearly distinguished. This is in contrast to a grand piano key action wherein the "set off" pressure is much greater and the "set off" point is more clearly distinguished. Because of this the key action of a grand piano has an improved "touch" which enables the player to control the strength and sound much more accurately.
It is an object of a first aspect of the present invention to provide an upright piano action which more clearly distingishes the "set off" point.
It is a further object of a first aspect of the present invention to provide a piano action which has improved repetitive playing characteristics.